In recent years, in explosion-proof facilities such as facilities where hazardous substances are handled or the like, clogging during the air feeding of combustible powders and clogging of sieves, as well as static charge build-up and discharge in the interiors of agitating tanks for organic solvents or the like whose inside surfaces are coated with Teflon, have become problems. Conventionally, in the case of static charge build-up and discharge inside such agitating tanks, the ignition of the organic solvents has been prevented by purging the air from the tanks with N2 gas, so that oxygen that might lead to ignition is eliminated. In the case of such de-charging methods, however, the initial costs and running costs of auxiliary facilities such as gas supply and exhaust facilities or the like are high, so that such methods are not desirable.
Meanwhile, air ionizing devices which neutralize electrical charges in charged bodies by means of ions have conventionally been used as devices for eliminating static electricity in production environments such as clean rooms or the like in which semiconductors, liquid crystal displays (hereafter referred to as “LCDs”) or the like are manufactured. Corona discharge type ionizers are commonly used as such air ionizing devices. In the case of such corona discharge type ionizers, a high positive or negative voltage is respectively applied to a positive or negative electrode, so that a corona discharge is generated, and the air surrounding the tip end of the abovementioned electrode is positively and negatively ionized; then, these ions are conveyed by air currents so that the charges on charged bodies are neutralized by ions of the opposite polarity.
However, semiconductor and liquid crystal manufacturing devices have become progressively smaller over the years, and in the case of conventional ionizers, it has become difficult to ensure an optimal installation space. Furthermore, the demand for static electricity countermeasures in narrow spaces such as the gaps between glass substrates inside cassettes and the like has also increased.
[Problems to Be Solved]
Accordingly, when the present inventors investigated the abovementioned reduction in size of air ionizing devices, and the application of such devices to explosion-proof facilities and equipment, the inventors found that the following problem points exist. Specifically, in the case of corona discharge type ionizers commonly used in the past, there is a considerable danger that the corona discharge itself will become an ignition source; accordingly, it has not been possible to use such ionizers in explosion-proof facilities such as facilities where hazardous substances are handled or the like.
Furthermore, in order to facilitate the generation of ions and prevent the consumption of generated ions, corona discharge type ionizers ionize the air in a state in which the electrodes are exposed in the vicinity of the object of de-charging. As a result, the following problems have also occurred.
(1) Generation of Ozone
Since the air in the vicinity of the object of de-charging is ionized by a corona discharge, a reaction which converts oxygen into ozone occurs besides the ionization of nitrogen and water vapor in the air. The surfaces of silicon wafers are oxidized by the oxidizing action of this ozone, and there are reactions with minute amounts of impurities in the air so that secondary particles are generated.
(2) Generation of Electromagnetic Noise
Irregular electromagnetic noise generated from the discharge electrode during the discharge may cause malfunctioning of precision instruments, computers or the like containing semiconductor elements.
(3) Generation of Dust from the Ion Generating Electrodes
The electrodes are consumed each time that a corona discharge is caused to occur, and the consumed electrode material is scattered. Furthermore, minute amounts of gas components in the air are converted into particles by the corona discharge, and are deposited on the ion generating electrodes, and when these particles reach a certain size, the particles are again scattered. As a result of such generation of dust, the yield drops.
In recent years, furthermore, ionizers which use soft X-rays as an ionization source have been developed. However, since the connecting parts between [such] ionizers and electrical cables, and the control devices for the ionization sources do not have explosion-proof specifications, it has been impossible to use such ionizers in explosion-proof facilities such as facilities handling hazardous substances or the like.